An annoying problem with a diesel engine is combustion noise. A major portion of the combustion noise is generated during the premixed phase and arises from the combustion rate of the diesel fuel when it first ignites after the ignition delay period. The ignition delay period is the period of time from the start of fuel injection into the combustion chamber until ignition occurs. The length of the ignition delay period is dependent on several factors: the quality of the fuel, cetane number, and cylinder temperature. Fuel that has been properly vaporized and mixed with air burns in a very rapid manner which causes high rates of pressure rise in the cylinders and subsequent high noise levels. The length of the ignition delay period influences the severity of the noise produced as it determines the amount of fuel that will be ready to be burned. The length of the ignition delay is strongly dependent on combustion chamber air temperature during the initial part of the fuel injection schedule. Diesels are normally a lot louder at high speed, low load conditions than at high speed, high load conditions. Ignition delay tends to get longer at low loads because the cylinder walls are cooler and as the air is compressed on the compression stroke it looses more heat so at the beginning of fuel injection the temperature in the combustion chamber is relative low which delays ignition. Ignition delay also gets longer because fuel systems spray quality is often lower at low deliveries and air density is lower which results in slower rates of fuel mixing and vaporization.
Thus, what is needed is an apparatus to reduce combustion noise by elevating the temperature of the air in a selected one of the combustion chambers so that at the start of the compression stroke the temperature of the air is elevated reducing the preestablished ignition delay period.
The present invention is directed to overcome one or more of the problems as set forth above.